FIG. 5 is a block diagram of a conventional angular velocity sensor 5001 disclosed in Japanese Patent Laid-Open Publication No. 2002-243451 (Patent Document 1). FIGS. 6 and 7 illustrate the waveforms of signals in the angular velocity sensor 5001. The angular velocity sensor 5001 includes a vibrator 2, a driver circuit 4 for driving the vibrator 2, and a detector 6 for detecting distortions produced in the vibrator 2. The vibrator 2 has any of various shapes, such as a tuning-fork shape, an H-shape, a T-shape, and a reed shape. Upon vibrating and rotating, a Coriolis force (an inertial force) is generated. The Coriolis force provides the vibrator 2 with a distortion. The distortion is electrically detected to calculate the angular velocity of the vibrator 2.
The vibrator 2 includes a vibrator element 2A mechanically vibrating, and a driver 8, a monitor 14, and sensors 10 and 12 which are provided at the vibrator element 2A. The driver 8 causes the vibrator 2 (the vibrator element 2A) to vibrate upon receiving a driving signal from the driver circuit 4. The sensors 10 and 12 outputs the distortion produced in the vibrator element 2A due to the Coriolis force resulting from the rotation of the vibrator element 2A as detection signals 501H and 501J, respectively. The monitor 14 detects the status of the vibration of the vibrator element 2A, and output the status as a monitor signal 501A. The detector 6 shapes the monitor signal 501A into a square waveform and outputs a shaped signal 501B.
The detection signals 501H and 501J generally contain distortion components representing the distortion produced in the vibrator 2 due to the Coriolis force and noise components. In the angular velocity sensor 5001, the noise components are removed from the detection signals 501H and 501J while only the distortion components are taken and used to calculate the angular velocity.
FIG. 6 illustrates the waveforms of the signals 501A and 501B and signals 1501C to 1501G which are carried in the noise components of the angular sensor 5001. FIG. 7 illustrates the waveforms of the signals 501A and 501B and signals 2501C to 2501G which are carried in the distortion components of the angular sensor 5001. The sums of the signals 1501C to 1501G and the signals 2501C to 2501G are denoted by signals 501C to 501G, respectively.
The detection signals 501H and 501J output from the sensors 10 and 12 are input to a differential amplifier 18. The differential amplifier 18 outputs a difference signal 501C, the difference between the signals 501H and 501J. A phase shifter 20 provides a shifted signal 501D by causing the difference signal 501C to shift (delay) in phase by 90 degrees. An inverter amplifier 22 inverts the shifted signal 501D to provide an inverted signal 501E.
A synchronous detector 24 synchronously detects the shifted signal 501D and the inverted signal 501E with reference to the shaped signal 501B as to output a detected signal 501F. A processor 26 smoothes the detected signal 501F to provide an output signal 501G. The angular velocity of the vibrator 2 is calculated from the output signal 501G.
The inverted signal 501E (the sum of the signals 1501E and 2501E) delays in phase from the shifted signal 501D (the signals 1501D and 2501D) due to the inversion amplifier 22. More specifically, the inverted signal 501E (the signals 1501E and 2501E) is not completely inverted from the shifted signal 501D (the signals 1501D and 2501D), and delays by a period T of time from the shifted signal 501D (the signals 1501D and 2501D). The detected signal 501F (the signals 1501F and 2501F) is smoothed to provide the output signal 501G (the signals 1501G and 2501G). The output signal 501G contains the signal 1501E (the signal 501E), an error caused by the period T, hence preventing the angular velocity of the vibrator 2 from being detected accurately.